Safe and arm device and method of using the same

ABSTRACT

A safe and arm device and method for a fuze in a bomb utilizing a piston and a drive shaft to rotate a rotor in and out of the safe and armed positions. The piston is operated by a difference in air pressure within the fuze as the bomb leaves its delivery vehicle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application claiming the benefit of a parentapplication, Ser. No. 11/100,234 filed on Mar. 31, 2005, the entiredisclosure of which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention described herein may be manufactured and used by or forthe government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefore.

FIELD OF THE INVENTION

The present invention relates generally to a safe and arm device, andmore particularly to a pressure activated safe and arm device and methodof using the same.

BACKGROUND OF THE INVENTION

The primary purpose of a safe and arm (S&A) device is to preventaccidental functioning of a main charge of explosive (military orotherwise) in a fuze prior to arming. Typically, in an electromechanicalS&A device, a sensitive primary explosive is physically separated from abooster explosive by an interrupter or barrier component. The barriercomponent, often a slider or rotor, interrupts the explosive path andthus prevents detonation of the booster and main charge prior to arming.Arming occurs by moving the barrier component to align the explosiveelements.

In some applications it is desirable to operate a safe and arm deviceaccording to a fluid pressure differential, such as in the event ofdropping a bomb from an airplane. But if there is a direct link betweenthe barrier component and the pressure differential then the device maybe sensitive to pressure fluctuations other than those meant to arm thedevice. Therefore, there is a need for a safe and arm device wherein thearming of the device is indirectly affected by the pressuredifferential.

SUMMARY OF THE INVENTION

An embodiment of the present invention includes a safe and arm devicefor a fuze in a bomb including an arming lanyard, with a first end ofthe arming lanyard attached to a delivery vehicle, and a second endattached to a manifold valve/firing pin, causing a translationalmovement of the manifold valve/firing pin when the bomb leaves thedelivery vehicle and causing the removal of a sealing plug and thebreaking of a shear pin. The translational movement of the manifoldvalve/firing pin opens an HP path for air movement into and out of ahigh pressure (HP) area and opens an LP path for air movement into andout of a low pressure (LP) area. The HP area and LP areas are separatedby a diaphragm mounted within the fuze. A piston is translationallymoveable within the fuze by a predetermined pressure acting upon thepiston caused by the entry of air through the manifold valve/firing pinas the bomb moves through the atmosphere. The translational movement ofthe piston is opposed by a biasing spring connected to the pistonpreventing movement of the piston until the predetermined pressure isattained and keeping the piston in a safe position when thepredetermined pressure is not obtained. The translational movement ofthe piston within the fuze compresses a drive spring positioned around adrive shaft attached to the piston, pushing against the drive shaftcausing a translational movement of the drive shaft. The drive shaft hasa plurality of driving balls residing in a plurality of hemisphericalindentations located around the drive shaft, the driving balls beingfree to move in said hemispherical indentations. A rotor is mountedaxially around the drive shaft so as to allow rotation of the rotorwithin the fuze from a safe position to an armed position. The rotor hasa plurality of electrically initiated detonators connected to aplurality of shorting contacts when the rotor is in the safe positionand aligned with a plurality of detonating contacts in the armedposition. The rotor has a plurality of helical grooves dimensioned andconfigured so as to accept the movement of the driving balls within thehemispherical indentations of the drive shaft caused by thetranslational movement of the drive shaft, wherein the rotor rotatesfrom the safe position to the armed position as the driving balls travelalong the helical grooves of the rotor. The device further includes anexhaust regulator located on the LP path, for adjusting a rate of airexhaustion from the LP area, thereby affecting the time required for therotor to rotate from the safe position to the armed position (the armingrate). The manifold valve/firing pin, upon impact of the bomb, with therotor in the armed position, drives against a plurality of piezocrystals connected to the electrically initiated detonators, the piezocrystals generating an electrical pulse directed to the detonatingcontacts via the electrically initiated detonators, thereby initiating adetonation of a plurality of explosive leads connected to saiddetonating contacts, thereby causing an explosion of the bomb.

Another embodiment of the present invention includes a method foroperating a safe and arm device for a fuze in a bomb, including creatinga translational movement of a manifold valve/firing pin by providing anarming lanyard, with a first end of the arming lanyard attached to adelivery vehicle, and a second end attached to a manifold valve/firingpin, causing a translational movement of the manifold valve/firing pinwhen the bomb leaves the delivery vehicle and causing the removal of asealing plug and the breaking of a shear pin. The translational movementof the manifold valve/firing pin opens an HP path for air movement intoand out of a high pressure (HP) area and opens an LP path for airmovement into and out of a low pressure (LP) area. The HP area and LPareas are separated by a diaphragm mounted within the fuze. The methodfurther includes providing a piston translationally moveable within thefuze by a predetermined pressure acting upon the piston caused by theentry of air through the manifold valve/firing pin as the bomb movesthrough the atmosphere; opposing the translational movement of thepiston by utilizing a biasing spring connected to the piston preventingmovement of the piston until the predetermined pressure is attained andkeeping the piston in a safe position when the predetermined pressure isnot obtained; compressing a drive spring positioned around a drive shaftattached to the piston due to translational movement of the pistonwithin the fuze, thereby pushing against the drive shaft causing atranslational movement of the drive shaft; providing a plurality ofdriving balls residing in a plurality of hemispherical indentationslocated around the drive shaft, the driving balls being free to move insaid hemispherical indentations; and rotating a rotor mounted axiallyaround the drive shaft so as to allow rotation of the rotor within thefuze from a safe position to an armed position. The rotor has aplurality of electrically initiated detonators connected to a pluralityof shorting contacts when the rotor is in the safe position and alignedwith a plurality of detonating contacts in the armed position. The rotorhas a plurality of helical grooves dimensioned and configured so as toaccept the movement of the driving balls within the hemisphericalindentations of the drive shaft caused by the translational movement ofthe drive shaft, wherein the rotor rotates from the safe position to thearmed position as the driving balls travel along the helical grooves ofthe rotor. The method further includes adjusting a rate of airexhaustion from the LP area utilizing an exhaust regulator located onthe LP path, thereby affecting the time required for the rotor to rotatefrom the safe position to the armed position (the arming rate); anddriving the manifold valve/firing pin, upon impact of the bomb, with therotor in the armed position, against a plurality of piezo crystalsconnected to the electrically initiated detonators, the piezo crystalsgenerating an electrical pulse directed to the detonating contacts viathe electrically initiated detonators, thereby initiating a detonationof a plurality of explosive leads connected to said detonating contacts,thereby causing the explosion of the bomb.

It is to be understood that the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not to be viewed as being restrictive of the present invention, asclaimed. The present invention is capable of other and differentembodiments, and its several details are capable of modifications invarious obvious respects, all without departing from the invention.Accordingly, the drawings and description are to be regarded asillustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side cut away view of the safe and arm device in the safeposition according to embodiments of the present invention.

FIG. 2 is a side cut away view of the safe and arm device in the armedposition according to embodiments of the present invention.

FIG. 3 is a side cut away view of the safe and arm device at the time ofimpact according to embodiments of the present invention.

FIGS. 4A-B are detailed views of the helical groove components of therotor of the safe and arm device in the safe position according toembodiments of the present invention.

DETAILED DESCRIPTION OF TH INVENTION

Before explaining the disclosed embodiments of the present invention indetail it is to be understood that the invention is not limited in itsapplication to the details of the particular arrangement shown since theinvention is capable of other embodiments. Also, the terminology usedherein is for the purpose of description and not of limitation. In thefigures the same reference numbers are used to identify the samecomponents.

Embodiments of the present invention include a launch sensing, fluidpressure activated safe and arm device for a fuze in a bomb and a methodof using the same that functions explosively when the proper targetenvironment is provided. The device utilizes a piston and a drive shaftto rotate a rotor in and out of the safe position. The piston isoperated by a difference in air pressure that enters the fuze as thebomb leaves its delivery vehicle.

FIG. 1 is a side cut away view of an embodiment of the present inventionin the safe position. The fuze 100 incorporates an arming lanyard 110that is attached to a delivery vehicle, such as an aircraft or anartillery piece. When the vehicle releases the bomb, the arming lanyard110, that is attached firmly to the delivery vehicle, translates amanifold valve/firing pin 112 and removes a sealing plug 116 from thehigh pressure inlet port 121 of the manifold valve/firing pin 112. Inaddition it causes the breaking of the shear pin 114 installed as asafety feature. This translation opens an HP (high pressure) path 210(shown in FIG. 2) for fluid (air) movement into and out of the highpressure (HP) area 120 and opens an LP (low pressure) path 220 (shown inFIG. 2) for fluid (air) movement into and out of the low pressure (LP)area 122 of the fuze's interior.

The fuze 100 incorporates a piston 128 and drive shaft 132 assembly thatis translationally moveable by a predetermined fluid (air) pressuredifferential acting on the manifold valve/firing pin 112 as the bombtravels. This fluid pressure differential is opposed by a biasing spring124, which substantially prevents movement of the piston 128 until thepredetermined required pressure is attained. The biasing spring 124 alsoassists in returning the rotor 118 to the safe position if the pressuredifferential is less than that required or if the pressure differentialsubsides from the predetermined required level. The required pressuredifferential ranges from about 4 to about 10 psi.

The piston 118 and drive shaft 132 are dimensioned so that a certainamount of travel of the piston 128 is necessary before movement thereofis transmitted via the drive shaft 132 to the rotor 118. Further, amovement-arresting detent mechanism is provided by the movement of thepiston 128 within the tubular section of the drive shaft 132, so thatmovement of the drive shaft 132 and rotational movement of the rotor isprecluded until there has been sufficient travel of the piston.

The drive shaft includes driving balls 134 as an integral feature, whichprovide a mechanical lock on the rotor 118 when in the safe position anddrive the rotor 118 to the armed position. The driving balls 134 arepartially received in hemispherical indentations 136 so that they arefree to move. The driving balls 134 are located adjacent to the insidesurface of the rotor 118. Additionally, the driving balls 134 arepartially received within helical grooves 144 defined by the peripheryof the axial bore of the rotor 118.

An embodiment of the present invention further includes a disk-shapedrotor 118 that is mounted to allow rotation from the safe position tothe armed position (shown in FIG. 2). Bearing balls 152 assist insupporting the rotor 118 as it rotates. The rotor 118 includeselectrically initiated detonators 138. When the rotor 118 is in the inthe safe position, the electrically initiated detonators 138 aremisaligned mechanically with the next component of the explosive firingtrain and electrically shorted to shorting contacts 140 to precludeinadvertent initiation from spurious electrical emanations.

The piston 128 and drive shaft 132 assembly is axially aligned with theinside axial bore of the rotor 118. Translational movement of the driveshaft 132 is converted to rotational movement of the rotor 118 by way ofthe driving balls 134. The inside bore of the rotor 118 contains helicalgrooves 144 that accept the placement and movement of the driving balls134. (See FIGS. 4A-B) The helical grooves 144 of the rotor 118 track thetranslationally driven driving balls 134, thereby imparting a rotationalmovement to the rotor 118. This arrangement of elements permits the safeand arm device not only to switch from a safe to an armed position, butalso from a partially armed to a safe position if a predeterminedpressure is not sensed or if the pressure differential acting upon thepiston 128 is raised above the predetermined magnitude but then fallsbelow the predetermined magnitude before the set arming time (discussedbelow) has transpired.

When the rotor 118 is in the armed position as shown in FIG. 2, theelectrically initiated detonators 138 are mechanically aligned withdetonating contacts 142 and electrically enable the explosive lead 150to receive a firing pulse from the piezo crystals 148 via the detonatingcontacts 142 when they are impacted by the manifold valve/firing pin112. The rotor 118 contains shorting contacts 140 which electricallyshort the electrically initiated detonators 138 in the safe position.The time required for the rotor 118 to translate from the safe to armedposition is selected by adjusting the rate of fluid exhaustion from theLP area 220 of the fuze assembly. This is accomplished by setting thegap of a needle valve on an LP exhaust regulator 146, which is placed onthe low pressure vent 154, so as to achieve the desired set arming timefor translation of the rotor 118.

FIG. 3 illustrates the safe and arm device at the time of impact. Onimpact the manifold valve/firing pin 112 is driven against piezocrystals 148 when the rotor 118 is in the armed position. The manifoldvalve/firing pin 112 is prevented from being able to contact the piezocrystals 148 when the rotor 118 is in the safe position by rotor lockpins (not shown). When the rotor 118 is in the armed position, thedriving balls 134 fit in the helical grooves 144 in the rotor, whichallows the firing pin 112 to translate through the rotor 118 and impactthe piezo crystals 148.

Upon impact the piezo crystals 148 generate an electrical firing pulse,which is directed to the electrically initiated detonators 138 viaelectrical leads to the detonator initiation contacts 142. This causesthe detonator initiation contacts 142 to be initiated and to propagateshock, high temperatures, and fragments to the explosive leads 150. Theexplosive leads 150 in turn propagate the next component in theexplosive firing train causing the explosion of the bomb. The explosiveleads are stationary and are an integral component of the housing.

In one embodiment of the present invention, to provide rotor positionalinformation, the rotor 118 is marked with an indicator, such as a decal,which defines the rotor position as safe or armed. The indicator isvisible from outside of the fuze housing via an optical element, whichis an integral component of the housing. In another embodiment, alocking mechanism operable via the HP inlet 121 or LP outlet 154 ports,provides a means by which the rotor 118 can be locked in either the safeor the armed position (for example the biasing spring 124 and drivespring 130 lock the rotor 118 in the armed position if the pressuredifferential equals the required pressure). In another embodiment, tocompensate for impact loadings to the device caused by conditions suchas either rough handling or momentary but extreme ambient pressurefluctuations, safeguard features such as a movement arresting mechanismhave been incorporated into the device. For example, the biasing spring124 and drive spring 130 hold the rotor 118 in the safe position if thepressure differential is less than the required pressure, or if thepressure differential subsides from the required pressure.

Although the description above contains much specificity, this shouldnot be construed as limiting the scope of the invention but as merelyproviding an illustration of an embodiment of the invention. Thus thescope of this invention should be determined by the appended claims andtheir legal equivalents.

1. A method for operating a safe and arm detonation device comprisingthe steps of: applying a pulling force to an arming lanyard attached toa sealing plug, wherein said sealing plug is in direct contact with afiring pin; releasing said firing pin by breaking a shear pin in contactwith said firing pin wherein said pulling force when applied to saidarming lanyard causes a first translational movement of said firing pinand said first translational movement of said sealing plug away fromsaid firing pin; opening a high pressure path for a high pressure airmovement into a diaphragm, wherein said high pressure air movement flowsinto and inflates said diaphragm when said sealing plug is removed awayfrom said firing pin; opening a low pressure path for a low pressure airmovement, wherein said low pressure air movement is caused by aninflation of said diaphragm; moving a piston in a straight line motionusing an inflation force generated by the inflation of said diaphragm;opposing the straight line motion of said piston using a biasing springin contact with said piston, said biasing spring opposing the straightline motion of said piston until a compression force which compressessaid biasing spring is attained; compressing a drive spring positionedin a drive shaft, wherein said drive spring is compressed by saidstraight line motion of said piston which pushes against said driveshaft causing a second translational movement of said drive shaft;rotating a rotor from a safe position to an armed position by convertingsaid second translational movement of said drive shaft to rotationalmovement of said rotor, wherein said rotor includes a plurality ofelectrically initiated detonators, said detonators being connected to aplurality of shorting contacts when said rotor is in the safe positionand aligned with a plurality of detonating contacts when said rotor isin said armed position, said rotor being axially aligned with saiddiaphragm, said firing pin, said biasing spring and said drive shaft;adjusting a rate of air exhaustion from a low pressure area connected tosaid low pressure path utilizing an exhaust regulator located withinsaid low pressure path, wherein said rate of air exhaustion determines atime period required for said rotor to rotate from said safe position tosaid armed position; and detonating said plurality of electricallyinitiated detonators with an electrical pulse generated by piezocrystals when said rotor is in the armed position and said piezocrystals are impacted by said firing pin which causes said electricallyinitiated detonators to detonate.
 2. The method of claim 1, wherein saidrotor includes an externally visible indicator providing rotorpositional information.
 3. The method of claim 1, wherein a lockingmechanism operable via said high pressure path or said low pressure pathprovides a means to lock said rotor in the safe position.
 4. The methodof claim 1, wherein safeguard features, including a movement arrestingmechanism, are incorporated into the safe and arm detonation device tocompensate for impact loadings to said safe and arm detonation devicecaused by rough handling or momentary but extreme ambient pressurefluctuations.
 5. The method of claim 1, wherein said rotor includes aplurality of helical grooves dimensioned and configured to acceptmovement of a plurality of driving balls which track within said helicalgrooves when said rotor rotates from said safe position to said armedposition.
 6. The method of claim 1, wherein said exhaust regulator is anadjustable pin valve.
 7. The method of claim 1, wherein the highpressure air movement into said diaphragm creates a pressuredifferential of about 4 to 10 pounds per square inch to compress saidbiasing spring.